Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $32.64   9.648%   $35.7891   $35.79   $35.80   $35.80  
  Purchase #2 $184.48   9.296%   $201.6293   $201.63   $201.65   $201.60  
  Purchase #3 $55.41   10.504%   $61.2303   $61.23   $61.25   $61.20  
  Purchase #4 $217.69   4.147%   $226.7176   $226.72   $226.70   $226.70  
  Purchase #5 $165.36   13.424%   $187.5579   $187.56   $187.55   $187.60  
  Purchase #6 $57.63   11.445%   $64.2258   $64.23   $64.25   $64.20  
  Purchase #7 $228.98   3.674%   $237.3927   $237.39   $237.40   $237.40  
  7 purchase totals = $942.19       $1,014.5427   $1,014.55   $1,014.60   $1,014.50